On 4 April 1968, Washington burned. As news of Martin Luther King's assassination spread, hundreds of African-Americans took to the streets, breaking windows, looting stores and starting fires. When the riots subsided four days later, large downtown areas of the capital lay in ruins. One of the few establishments spared along U Street, where the riots began, was Ben's Chili Bowl, a small diner owned by Ben Ali, who has died aged 82.

Ben's Chili Bowl has stood at the centre of Washington's transformation over the last 50 years. Ali opened the restaurant in a former silent film theatre in August 1958 together with his fiancee, Virginia Rollins, whom he married a few weeks later. It was part of America's Black Broadway, the thriving business and entertainment district along U Street. After the riots, the black middle class fled, and the neighbourhood became a hotbed of crime and drug addiction through the 1980s and 90s. The Chili Bowl survived the lean years, however, and has witnessed the area's recent revitalisation and gentrification. Historic theatres such as the Lincoln, next door to Ben's, have been restored to their former grandeur. The empty lots and burnt-out buildings are now mostly gone, replaced by luxury flats.

Ben's still caters to the masses, though. Its decor and menu remain largely unchanged since the 1950s – but more vegetarian options have been added. Construction workers come for breakfast in the morning, and after the bars have closed at night, partygoers form a queue out of the door for french fries, milkshakes and Washington's signature "half-smoke" – a smoked beef and pork sausage – smothered in chili. Earlier this year, Bon Appetit magazine named Ben's the best chili spot in America.

Bill Cosby, the comedian and actor, was a patron during the diner's early years, when he was in the US navy and stationed in Washington. Cosby brought his wife Camille Hanks to Ben's on their sixth date, and proposed to her there. For years, a sign inside read: "Who eats free at Ben's: Bill Cosby. No one else."

That was changed last year, during the US election, to: "Who eats free at Ben's: Bill Cosby. The Obama Family." In January, shortly before his inauguration, Barack Obama had lunch at Ben's with Washington mayor Adrian Fenty (Obama paid $20 on a $12 tab). Indeed, Ben's has become something of a mandatory stop for politicians, both local and national. Photographs of Jesse Jackson and Al Sharpton decorate the walls next to shots of celebrity guests such as Bono and Serena Williams.

Ali, whose grandparents were from northern India, was born in Trinidad and went to the US in 1945 as a student. "I came here to become a doctor," he told the News India-Times in February. "I knew Shakespeare, Chaucer, Wordsworth. I had studied in the British system. I could quote any of the poets." After graduating from the city's Howard University, however, he dropped out of dental school and tried a variety of careers, including importing and property, before opening the Chili Bowl. His chili recipe is a family secret. Coming from the Caribbean, he thought American foods were bland, and believed there would be a market for spicier fare. As a Muslim, however, he never ate the half-smokes.

During the 1968 riots, Stokely Carmichael, the leader of the Student Nonviolent Co-ordinating Committee (SNCC), led protesters along U and 14th Streets and told business owners to close their shops out of respect for King, as they had after John F Kennedy was assassinated. But Carmichael asked Ali to keep his diner open. The SNCC offices were across the street, and the Chili Bowl became the place where the protesters, police and firefighters could meet (and eat). During the height of the violence, Ali used a bar of soap to write "Soul Brother" on the window – a sign to looters that his was not a white-owned business.

In 1996, Ali and Virginia decided to step back and leave the restaurant in the hands of their sons Nizam and Kamal, who had worked there as children. They expanded the business, opening a second location at the city's baseball stadium, and a higher-end restaurant next door. Ali is survived by Virginia and their three sons.